1. Field of the Invention
The invention relates in general to a focusing controller and the method thereof, and more particularly to a focusing controller and the method thereof used in an optical disk drive.
2. Description of the Related Art
Focus error signal Fe is used to adjust the position of pick up head of an optical disk drive so as to focus the laser beam emitted by the pick up head onto a currently loaded optical disk. FIG. 1 is a block diagram showing a convention optical disk drive 100, which includes a focusing controller 120 and a pick up head 110 used for accessing an optical disk 130. After the focus error signal Fe being derived according to the reflected light from the optical disk 130, the focusing controller 120 outputs a focus control signal Foo to control the pick up head 110 according to the focus error signal Fe.
FIG. 2 is a block diagram showing the focusing controller used conventionally, which basically includes an analog-to-digital converter (A/D converter) 210, a focus compensator 220 and a digital-to-analog converter (D/A converter) 230. The A/D converter 210 receives and digitizes the focus error signal Fe and delivers a digital focus error signal to the focus compensator 220. The D/A converter 230 then converts signal at the output terminal of the focus compensator 220 to generate required focus control signal Foo for controlling the position of the pick up head 110.
However, noises inside the optical disk drive affect the servo signals, including the focus error signal, so that the laser beam cannot precisely focus on the optical disk. There includes a plurality of tracks having pits and lands thereon used to record information on the surface of an optical disk. However, the focus error signal Fe is easily coupled with the track error signal Te during tracking operations, which indicates that the pickup head may not be allocated at an accurate position during the following focusing operations since the currently derived focus error signal Fe is erroneous because of coupling low-frequency error component from the track error signal Te. FIG. 3 shows waveform diagrams of the track error signal Te and the focus error signal Fe during tracking operations. Obviously, the focus error signal Fe is usually coupled with the low-frequency component of the track error signal Te such that the actually focus status of the pickup head may not obtained due to an erroneous Fe is derived.